Production of liquid hydrocarbons from rice crop wastes mixtures by co-pyrolysis and co-hydropyrolysis

• Co-pyrolysis of rice husk and straw blended with PE (polyethylene) led to liquids with more oxygenated compounds.
• The rise of rice biomass content on PE blends led to an increase in CO and CO2 in co-pyrolysis gases.
• Study of co-pyrolysis liquids upgrading by hydropyrolysis (with H2) after co-pyrolysis.
• Co-hydropyrolysis led to the highest conversion and to the highest gas and liquid yields.

The aim of this work was the valorisation of rice crop wastes mixtures by pyrolysis to produce liquids to be used as bio-fuels or as raw bio-materials. The effect of waste mixtures composition on liquids yield and composition was studied. Rice husk (RH) and straw (RS) were pyrolysed with polyethylene (PE), the main plastic used in rice production process. Polypropylene (PP) and polystyrene (PS) were also studied, due to their presence in great amounts in solid wastes. The rise of rice husk amount in PE blends led to a decrease in the conversion of co-pyrolysis (pyrolysis of blends of biomass rice and plastic wastes) and to a reduction of liquid yields. Thus, the blend with 20% (w/w) of rice wastes was selected for further studies. No great changes were observed in the results when husk was replaced by straw, which is advantageous for the pyrolysis process. However, the same was not observed for the type of plastic waste. PS decreased total conversion and the formation of gases and liquids and increased aromatic compounds content in liquids. Some tests were done using hydrogen (hydropyrolysis) instead of nitrogen (pyrolysis) with the aim of improving liquids quality due to the presence of hydrogen in the reaction medium. Different pathways were analysed: (I) co-pyrolysis; (II) co-hydropyrolysis; (III) co-pyrolysis followed by hydropyrolysis and (IV) hydropyrolysis of co-pyrolysis liquids. Co-pyrolysis followed by hydropyrolysis was not favourable for further solids conversion and led to a great increase of gases. Co-hydropyrolysis led to the highest conversion, as both gas and total liquid yields increased.